Spacline,
I have no personal experince of resperidone.
However I may be able to give you some information on the Licencing issues (I used to work in the pharmaceutical industry).
Hardly any drugs are specificaly licenced for use in children. The reason for this is quite simple, no-one would put their kids into a clinical trial! And you cannot get informed consent in a child, and without that you can't enter them in a trial (simplification of the situation a bit, I know, but that this the general gist of things.)
It is very, very common to use things 'off licence'. For example antidepressants are used very sucessfully to treat pain, not licenced but works very well, and people have been doing it for years. Some medications for epilepsy are used to treat trigeminal neuralgia. Treatments for meonopausal women are used to treat girl babies with fused labia!. The paperwork costs of getting these extras on the licence are large and drug companies will often not bother to get the licence changed. In these situations they cannot market the drug for off licence use, but they are used every day, often with great sucess.
No-one can say to you that treatment is without risk, nothing in life is without risk, leaving your son intreated will have risks of its own (as I sure you know).
Get as much information as you can, and talk to your docs. Hope things get better soon for you and your son.